Radiators heating when room thermostat is turned down

[dementedpixie]

@PigletJohn don't know of this is within your expertise but hopefully if not someone else can help.

I have a conventional boiler with feeder tanks and a hot water cylinder. I have noticed recently that even when my room thermostat is turned down to 12⁰C my heaters are coming on full blast especially in the morning (don't know whether that's because the hot water is also in at the same time at that point)

Is this a valve issue maybe?
Do I need an engineer to come and check it out?

Normally there are some valves (two I think in my case) that switch the heating water circuit to one of three configurations, heating only, hot water only, hot water and heating.

It sounds like one of the valves may not be working.

First does the heating come on if the hot water is not activated as you say ?

Second, sometimes the valves have levers on top that you can see move when the valves are activated. They move slowly from one configuration to the other when you switch on the hot water or heating. Might be worth checking whether you can see these in action.

The valves are controlled by the heating controls, so it is possible that there is a problem with the heating control output rather than the valve.

We had this recently & it was a valve

Would the valves be near the boiler or near the hot water cylinder? The boiler is actually only a year old and i do think the issue happened intermittently before we got it replaced so I'm thinking it's not a boiler issue as such but is in a different area

Ours was in the hot water tank, but I'm no expert!

They are usually next to the hot water cylinder.

Mine are next to the hot water cylinder on some pipework in front of it.

They are small boxes a few inches square with leads coming off them and attached to the pipes. The leads go to the heating controller.

I'll have a look tomorrow. It involves removing a wooden front bit to access the cylinder in the cupboard

We had this too and it was the two point valve that had gone bad and would not close so the heat stayed on even after you’d turned it off. The valve is by the hot water cyclinder.

In the interim, what does work is putting the boiler into standby or turning it off.

Possibly completely different, but our UF heating wouldn't turn off, turned out to be a battery in the wall thermostat that needed changing - it wasn't sending the signal to turn off.

The valve is often near the pump, either close to the boiler, or near the hot water cylinder. They typically last 20 years or more. Here are some examples to look for

https://www.screwfix.com/search?search=Port+valve&brand=drayton|honeywell_home

In some more modern boilers they are inside the boiler casing and need a boiler repair person.

Combis have a diverter valve inside.

Oh, and some systems decide themselves what do do, according to the weather.

@PigletJohn if its near the hot water cylinder then nothing in the that cupboard has been changed since the house was built in 2000 so will be 23 years old. I will investigate the cupboard today

And even with my thermostat at 10⁰C my heaters were hot this morning. I really think it must happen when the hot water and heating are on together. I usually have both on a timer and use the thermostat to control whether the heaters come on. Hot water is only on for 1 hour, 6-7am.

I'm guessing the red thing is the pump and the blue thing might be the thing causing the issue.

I have someone coming to look at at on Thursday but like to know what the problem might be

Well could be stuck valve (I think the blue box) - like I say on my system there are 2x. Then it could be power to the valve which may come from that grey box that appears to be floating around (I thought 2000s era wiring standards were better than that, to me it should really be fixed securely to a surface) or it could be the line from the heating controls that tells the valve to switch.

It's possible I guess that if all the power in there (immersion heater, valve actuation etc) is attached to a single breaker in the consumer unit/fuse box that that breaker has tripped and is what is stopping the valve actuating.

The integrity of the wiring doesn't look great, I wouldn't touch it unless you know what you are doing. If you are electrically qualified it should be a relatively simple job to switch the motor head over if you can diagnose it. See some stuff on youtube such as this.

I'm certainly not touching the wiring and yes it doesn't look great. Think they flung these houses up without much care as there's been other issues with plumbing in the loft too.

Yes, the red thing is the pump, the blue thing is a motorised valve, the grey box is a wiring centre and should have been screwed to the wall, not dropped on the floor.

But I think I can only see two pipes on the valve (an in and an out). I was expecting three, arranged in a T shape, so the hot supply goes in and is sent to the cylinder, or to the rads, or to both. Does it have three pipes? If not, is there another motorised valve somewhere?

You sometimes come across heating people who say there is no need, the TRVs will prevent radiators being heated if the rooms are up to temp. I don't share that view.

Depends whether it is an S type or a Y type heating system.

Y has a single 3 port valve.

S has two dual port valves. Mine is S type. Maybe the second valve is hidden behind that box or somewhere else. I wouldn't poke around in there too much though - don't like the look of the wiring.

Mine does this when the batteries in the thermostat die

My room thermostat is wired into the mains

Glad to hear it. Wired stats hardly ever go wrong.

Just to update; it was the diverter valve thingy and I am now the proud owner of a new one. Seems to have tidied up the electrical box a bit too

So is ours, but a battery is still required to send on/off signals.

Glad you got it resolved.

Good stuff. I've learnt enough from this thread to replace my motor heads when they go.

The one on the radiator circuit says Expires 04/2012 on it, so a little past its use by date.

By the time they are 20 years old, the rubber ball inside the brass valve may be worn out, so changing the motor head (which is a simpler job) may not be enough. Changing the entire valve is a wet plumbing job and will require a partial drain down.